1. Field
This disclosure relates to routing queries in packet-based networks, more particularly to a method for allowing a route re-query in H.323 and SIP (Session Initiation Protocol) networks.
2. Background
In H.323 networks, entities referred to as endpoints query a gatekeeper for admission to the network for a call. These endpoints, such as endpoints, typically use Registration, Admission and Status (RAS) admission requests, typically abbreviated as ARQ. The gatekeeper responds with admission confirm (ACF) messages that contain the routing information necessary for the originating endpoint to make call attempts to the destination.
When the gatekeeper receives the admission request, it may access another device or function, such as a routing server, that contains the routing information on possible routes between the originating endpoint and the destination endpoint. The ACF message transmits this routing information to the originating endpoint. For example, the ACF message may contain the Internet Protocol (IP) address for the destination endpoint.
The originating endpoint receives the ACF message and attempts to make a call to the destination endpoint specified in the message. However, in most current implementations of this type of exchange, if the call attempt to the destination fails, the call is released by the originating endpoint and the call fails.
In some instances, the gatekeeper may provide alternate destination endpoints in the ACF message. The endpoint should attempt to establish calls with these alternate endpoints if the initial attempt should fail. However, some limitations of the alternate endpoints exist. For example, different destinations may require different source or destination information to appear in the setup message transmitted to establish the call. As this information cannot be carried in the ACF message, the originating endpoint cannot use it, which will cause the call to fail. This results in alternate endpoints that are not feasible endpoints for the call.
Another limitation may reside in security information needed for each alternate endpoint. In order to utilize these endpoints, the originating endpoint would be required to generate the security information for each endpoint provided. As calls are normally completed to the initial destination, the overhead costs of generating this information may be considered too expensive when compared with the probability of actually employing it.
In other networks, such as SIP networks and even H.323 networks that utilize the Gatekeeper routed call signaling model, routing information may be determined by intermediate signaling entities, such as SIP proxies or routing Gatekeepers, by communicating directly with the routing function without involving the endpoint in subsequent route re-queries and subsequent call setup attempts. The use of RAS from an H.323 endpoint to a Gatekeeper that communications with a routing function is one just one topology that is part of this invention.